Advances in IR imaging technologies for high-resolution wide-area surveillance are driving small pixel, high-density, large-format infrared (IR) focal plane arrays (FPAs). However, conventional metal contacts and metal grid lines used in prior art 3D heterogeneous integration partially cover the active area of a pixel, decreasing fill factor and quantum efficiency (QE).
U.S. patent application Ser. No. 14/183,237, filed Feb. 18, 2014, which is incorporated herein by reference as though set forth in full, describes IR-transparent ohmic contacts and interconnects and silver nanowire (Ag NW) network based Infrared-transparent conductors (ITCs). Ag NW-based ITCs, however, have decreasing optical transmittance with increasing wavelength due to reflections, which are quite significant for long wavelength infrared (LWIR). Also Ag NW networks are porous, which is not ideal for making contacts on small (sub-wavelength-sized) IR pixels operating at long wavelength infrared (LWIR) wavelengths.
The prior art for IR-transparent conductors includes the following. “Widely transparent electrodes based on ultrathin metals”, Optics Letters 34, 325 (2009), incorporated herein by reference, describes ultra thin 2 nanometer (nm) Ni films with a resistivity of ρ˜200 μΩ cm (Rs˜1 kΩ/sq.), and an optical transmittance Tλ of about 82% over a 400 nm-25 μm wavelength range. “Transparent, Conductive Carbon Nanotube Films”, Science 305, 1273 (2004), incorporated herein by reference, describes a 50 nm thick single walled carbon nanotube (SWNT) film deposited on a quartz substrate, which provides Tλ>70% in the visible and Tλ˜80%-95% in near infrared (NIR) with ρ=150 μΩ cm (Rs=30 Ω/sq.), and also describes a 240 nm thick SWNT free-standing film, which provides Tλ˜6-35% in the visible and Tλ ˜6%-86% over a 400 nm-20 μm wavelength with no information on ρ or Rs. “Infrared transparent carbon nanotube thin films”, Appl. Phys. Lett. 94, 081103 (2009), incorporated herein by reference, describes a 25 nm thick carbon nanotube (CNT) film deposited on a quartz substrate, which provides Tλ ˜70-82% in the visible, Tλ ˜82%-94% in Near Infrared-short wave infrared (SWIR), and Tλ ˜94%-85% in 2.5 μm-20 μm wavelength range with Rs=200 Ω/sq.
“Prospects for nanowire-doped Polycrystalline graphene films for ultratransparent, highly conductive electrodes”, Nano Letters 11, 5020 (2011), incorporated herein by reference, describes a theoretical simulation predicting Rs and Tλ in the visible spectrum for a hybrid system using Ag NW doped with graphene, and describes such a hybrid system for high performance transparent conductors. The simulation results indicate that both Rs and its variation can be significantly improved by using the hybrid system without a loss of transmittance. “Improved electrical conductivity of graphene films integrated with metal nanowires”, Nano Letters 12, 5679 (2012), incorporated herein by reference, describes graphene films integrated with Ag NWs that provide Rs=30-80 Ω/sq. for Tλ˜90% at 550 nm. “Hybrid Transparent conductive film on flexible glass formed by hot-pressing graphene on a silver nanowire mesh”, ACS Applied Materials & Interfaces 5, 11756 (2013), incorporated herein by reference, describes a hot-pressed graphene film on an Ag NW mesh prepared on a flexible glass substrate, demonstrating Rs˜14 Ω/sq. and Tλ˜90% at 550 nm.
“High-performance, Transparent, and stretchable electrodes using Graphene-Metal nanowire Hybrid Structure”, Nano Letters 13, 2814 (2013), incorporated herein by reference, describes Ag NW-graphene hybrid films which provide Tλ˜94% in the 400 nm-1.5 μm wavelength range with Rs˜33 Ω/sq., and describes Ag NW-graphene hybrid electrodes fabricated on an InZnGaO (IZGO) film.
Although the prior art describes electrical contacts and interconnects that are transparent for some wavelengths, what is needed is electrical contacts and interconnects, and/or grids that are transparent over visible to LWIR wavelengths. The embodiments of the present disclosure address these and other needs.